StringToSliceHookFunc only works on slice of strings

[vincentbernat]

Hey!

Since 84b9bc9, StringToSliceHookFunc() only works when the target is a slice of strings. Previously, it worked for any slices, notably slices of int for example.

		if f.Kind() != reflect.String {
			return data, nil
		}
		if t != reflect.SliceOf(f) {
			return data, nil
		}

Since f is a string value because of the first condition, the target has to be a slice of strings.

I'll propose a PR shortly to fix that.